Since mental illness is treated in both the specialty mental health and the primary medical care sectors, it is necessary to clarify the roles of each in a comprehensive service delivery system. It is particularly vital to document the quality of diagnosis and treatment in each sector's routine practice because of its implications for public policy and national performance standards. This study will investigate clinicians' routine diagnosis and treatment of depressive disorders through a minimally intrusive research design. A cohort of 150 patients will be identified at each of three community mental health centers and three primary medical care centers as "possibly depressed" on the basis of their CES-D cores. The Diagnostic Interview Schedule, whose validity is now being established, will then be administered to these persons. Research diagnoses derived from it will be compared with diagnoses assigned by clinicians to these patients. Clinicians will be kept blind about degree of diagnostic agreement, and their treatment of these patients will be monitored over a six-month period. Through followup interviews, we then will assess each patient's level of depressive symptomatology, social adjustment, and satisfaction with treatment. Scores on these dimensions will be related to clinician diagnosis and agreement/disagreement with the research diagnoses. Estimated cost per episode of care will be similarly related to clinician agreement/disagreement with the research diagnosis, as well as to patient characteristics and the caregiving sector within which treatment occurred.